The present invention relates to an apparatus for mounting electronic components with leads onto a circuit board substrate by inserting the leads of the electronic components in corresponding holes in the circuit board substrate, and further to a method and device for detecting the attachment of electronic component with leads to the circuit board substrate.
Mounting of an electronic component with leads onto a circuit board substrate is generally achieved by an action for fixing leads of the electronic component 20 to the circuit board 22 as shown in FIG. 9. Leads 21 of the electronic component 20 are inserted into corresponding holes 29 formed in the circuit board 22. A clinch means comprising a clinch lever 25 and a clinch bed 26 is moved to below the holes 29 in which leads 21 have been inserted. The tip of the lead 21 which has pierced through the circuit board 22 to the backside thereof is cut to a predetermined length by the clinch lever 25 moving toward the clinch bed 26. The lead 21 is clinched against and fixed to the circuit board 22 by further movement of the clinch lever 25.
A piezoelectric element 1 is attached to the clinch lever 25 for detecting stress-strain which is generated in the clinch lever 25 at the time of cutting and clinching the lead 21. From the stress-strain amount detected by the piezoelectric element 1, it is detected whether the electronic component 20 has correctly been mounted onto the circuit board 22. If the leads have not been inserted or pierced through the holes 29, or have been bent when being inserted into the holes, the clinch lever 25 accordingly receives less load. On the other hand, if the leads are properly inserted in the holes, the clinch lever 25 receives a great load upon cutting and clinching the leads, whereupon the piezoelectric element 1 detects large stress-strain. Therefore, the detected stress-strain of the clinch lever reflects the quality of the attachment of the electronic component 20 to the circuit board, and thereby it is detected whether the electronic component has been mounted in a favorable condition. For this purpose, the piezoelectric element 1 is connected to an insertion detecting circuit shown in FIG. 10.
Referring to FIG. 10, the stress-strain that is generated in the clinch lever 25 is detected by the piezoelectric element 1, and an electric signal proportional to the amount of detected stress-strain is amplified by a differential amplifier 32. A xcfx80 filter 33 is provided for cutting high frequency component from the electric signal sent from the differential amplifier 32 so as to remove noise components mixed at the piezoelectric element 1. The electric signal from which noise components have been removed is amplified by a variable gain amplifier 34, so that it is compared by a voltage comparator 35 with a threshold which is a reference for judging whether the leads 21 of the electronic component 20 have properly been inserted in corresponding holes. The voltage comparator 35 is a circuit designed for comparison of an inputted voltage with a reference voltage (threshold). The threshold as the reference voltage can be preliminarily set, so that the voltage inputted from the variable gain amplifier 34 is compared therewith, and when the inputted voltage is greater than the threshold, the voltage comparator 35 changes its output voltage accordingly. With this change in voltage outputted from the voltage comparator 35 as a trigger, a monostable multivibrator 36 outputs a pulse, which is in turn inputted into the electronic component mounting apparatus from an output terminal 38 via a transistor 37. The apparatus thereby judges whether the electronic component with leads has correctly been fixed on the substrate.
There is now remarkable diversity in electronic components and component with leads is no exception. Therefore, diameter and material of the leads, and shearing stress necessary to cut the leads also come in many varieties. In the conventional insertion detecting circuit described above, however, the threshold for judgement by the voltage comparator 35 is set to a constant voltage. Upon changes to the diameter, material, or shearing stress of the leads, the stress-strain that occurs in the clinch lever 25 changes as well as the amount of stress-strain detected by the piezoelectric element 1. Accordingly, the judgement by the voltage comparator 35 was sometimes incorrect. Misjudgment also occurred in the cases such as when the clinch lever 25, clinch bed 26, or the piezoelectric element 1 was replaced, when the shape of the clinch lever 25 or clinch bed 26 varied, or when the piezoelectric element 1 having characteristics suitable for one type of apparatus was applied to a different type of apparatus.
In order to deal with such problems, it was necessary to change the preset threshold voltage in the voltage comparator 35, or to effect gain adjustment of the variable gain amplifier 34. However, such operation for changing the settings was not easy, and it is not realistic to change the settings of the circuit in accordance with changes in the stress-strain detected by the piezoelectric element 1. Not to mention, if the diameter, material, or shearing stress of leads on an identical electronic component differs, such could hardly be dealt with.
An object of the present invention is to provide a method and device capable of correctly judging whether an electronic component with leads has properly been fixed on a circuit board substrate with its leads being inserted in corresponding holes in the circuit board substrate.
In order to achieve the above objects, the present invention provides a method of mounting an electronic component with leads on a substrate, wherein the leads of the electronic component are inserted into corresponding holes formed in the substrate, and clinched with a clinch means so that the electronic component is fixed on the substrate, characterized by comprising the steps of:
selecting a standard reference value for determining whether or not the leads of the electronic component have been inserted in the holes, said standard reference value being selected based on values representative of characteristic features of the electronic component with leads such as diameter, material, or shearing stress of lead;
detecting stress-strain generated in said clinch means; and
comparing a detected stress-strain with the selected standard reference value, whereby it is determined whether or not the electronic component with leads has been mounted to the substrate.
The apparatus for mounting an electronic component with leads on a substrate, according to the present invention, comprises an insertion head for inserting the leads of the electronic component into corresponding holes formed in the substrate, a clinch means for clinching the leads that are inserted into the corresponding holes for mounting the electronic component to the substrate, a detecting means for detecting stress-strain generated in the clinch means, and a judging means for determining whether or not the electronic component with leads has been mounted on the substrate based on a detected result obtained by the detecting means, and is characterized in that:
the judging means includes a plurality of threshold values that are preset therein, and comprises a threshold output means that is capable of selectively outputting one of these threshold values as a standard reference value for detecting the attachment of the electronic component to the substrate, a threshold selecting means for selecting one of the threshold values in accordance with the type of electronic component with leads which is to be mounted to the substrate, and an insertion detecting section which compares a detected result obtained by the detecting means with the selected threshold.
The present invention further provides a method of detecting the attachment of an electronic component with leads to a substrate, wherein the leads of the electronic component are inserted into corresponding holes formed in the substrate, and clinched with a clinch means so that the electronic component is fixed on the substrate, characterized by comprising the steps of:
selecting a standard reference value for determining whether or not the leads of the electronic component have been inserted in the holes, said standard reference value being selected based on values representative of characteristic features of the electronic component with leads;
detecting stress-strain generated in said clinch means; and
comparing a detected stress-strain with the selected standard reference value, whereby it is determined whether or not the electronic component with leads has been fixedly attached to the substrate.
The device for detecting the attachment of an electronic component with leads to a substrate according to the present invention is characterized by having
a threshold outputting section in which a plurality of threshold values are preset as standard reference values for judging whether the insertion of the leads to the holes has been successful or not, and which is capable of selectively outputting one of the threshold values,
a threshold selecting means for selecting one of the threshold values,
a detected threshold outputting section for outputting a detected value representative of the stress-strain in the clinch means, that is outputted from the detecting means, and
an insertion detecting section for comparing the detected value with the selected threshold value, and for outputting an insertion detecting signal when the detected value exceeds the threshold value.
According to the present invention method and device, the standard reference value or a threshold voltage is suitably selected in accordance with differing diameters, materials, or shearing stresses of leads. A detected voltage representative of stress-strain that occurs in the clinch lever is compared with this reference value, for the judgement of whether the insertion of the leads of an electronic component into the holes in a circuit board has been successful or not. Thus the determination of the attachment of an electronic component with leads to a circuit board can correctly be performed.